The Conservatives have called for every asylum seeker to be kept in secure centres until they have been investigated by the security services.

Party leader Iain Duncan Smith launched a scathing attack on the current immigration system which allowed "someone with evil intent" to enter Britain unchecked.

He made the controversial policy announcement in response to the recent arrests of terrorist suspects and claimed the government was "incapable of asserting itself as the guardians of security".

Duncan Smith insisted the checks are a necessary part of the war against terrorism.

"The message to terrorists must be this: stay at home or you will be sent home," he said.

"We cannot pretend there is no problem. We have to play our part as a member of the international community but we must also protect our domestic security."

The Tory leader highlighted the current state of high security.

"That requires security vetting of all people claiming asylum in the UK. That vetting should be conducted quickly and efficiently and it must be done in secure conditions," he said.

"No one should be allowed on our streets unless we are satisfied they pose no threat to other occupants of our streets."

Oliver Letwin, the shadow home secretary, argued that fanatics with terrorist links were exploiting loopholes in a disorganised system.

"Terrorists know that they can gain access to Britain by taking advantage of our chaotic asylum system," he said.

"This cannot be allowed to go on, especially at this dangerous period in our history. An asylum system that is not safe and is not fair cannot last in a democracy."

The Conservatives also called for an "urgent review" of all asylum treaties, including the 1951 Geneva Convention.

The Liberal Democrats slammed the announcement as an attempt to grab headlines.

The party's home affairs spokesman, Simon Hughes, accused Duncan Smith of making a "scapegoat" of asylum seekers.

"The weakness of the UK's asylum policy is not in its legislation, but in its administration," he said.